If "Transforming Sphere" is equipped with a monster like "Vanity's Fiend" or with a Special Summon Monster like "Dark Armed Dragon" that cannot be Special Summoned, then during the End Phase the effect to Special Summon the equipped monster to your opponent's field still activates. However, the monster cannot be Special Summoned, so it is sent to the Graveyard. Similarly, if you cannot Special Summon during the End Phase - for example, if the effect of "Vanity's Fiend" is active, or if you activated "Scapegoat" during this turn - then the effect of "Transforming Sphere" still activates during the End Phase, but the equipped monster is sent to the Graveyard since it cannot be Special Summoned.[6]

A monster like "Dark Armed Dragon" or "Judgment Dragon" cannot be Special Summoned, except by the method stated in its text. It cannot be Special Summoned by effects like "Monster Reborn", even if it was properly Special Summoned beforehand. Also, you cannot Special Summon "Dark Armed Dragon" from the Graveyard even if there are exactly three DARK monsters in the Graveyard.[7]

Previously Official Rulings

These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami.[10] They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: [11][12][13][14][15][16][17][18][19]

"Dark Armed Dragon" can still be Special Summoned while there are non-DARK monsters in your Graveyard.